Recombinant preparations offer various advantages over those based on natural allergen extracts. Recombinant proteins can be produced in highly purified forms of pharmaceutical quality; proteins are molecularly defined thus ensuring product consistency and minimising problems related to allergen extract standardisation; preparations only include those proteins that are considered relevant for specific immunotherapy; the risk of contamination with other allergenic material is excluded; the whole production process can be designed to exclude any risk factors for the introduction of infectious agents; the relative dosages of individual components of a final preparation can be optimised to favour better clinical efficacy. Allergy vaccination (AV) mediates the immune response to allergen exposure by altering the TH2 response in favour of a TH1 T-cell response, increasing IgG production and decreasing the production of inflammatory cytokines. rBet v1-FV is an AV designed to enhance beneficial immune responses. The investigational product has demonstrated efficacy and good tolerability in one previous pivotal Phase III and two previous Phase II studies.